This is very common in new layers, I had all kinds of strange soft shelled eggs, then things got regular. Occationally now my golden sex links(10 mos old) instead of taking a day off will pop out a soft shell and then things resume to a nice regular egg again. If your pullet is new to laying no worries unless it continues, oyster shell is a good idea to supplement, but even with oyster shell new layers take a while to work out the kinks and get regular with their laying.....The "double yolks" and "double eggs" "soft shells" are usually the ovaries misfireing or the oviduct speeding up or slowing down the process...